ABSTRACT
In this paper, we report on the enhanced control of resistive switching in multilayer Si/SiO2 structures, which permit the formation of Si nanocrystals with a typical size of 5.88 nm and overall good shape homogeneity. The deposition of a different number of Si and SiO2 bilayers (6, 8 and 10) allowed control of SET/RESET voltages in negative bias ranges 4.5-10 V and 6.3-13 V for six- and ten-bilayer devices, respectively. The corresponding resistance ratio between ON/OFF states varied in the ranges 107-105 for the aforementioned number of bilayers. Based on the result of XPS measurements, we suggest that the resistive switching in the studied system occurs due to the formation and annihilation of Si-Si and Si-O bonds, which serve as conductive pathways and isolating material, respectively.
ABSTRACT
Er3+-Yb3+ co-doped phosphate glasses containing silver nitrate (SN), were fabricated. Transmission electron microscopy (TEM) and x-ray photoelectron spectroscopy (XPS) analyses were used to evidence the nucleation and presence of silver nanoparticles (SNP). The basic parameters of the glasses were inspected by means of absorption and fluorescence spectra, and fluorescence lifetimes under excitation at 916 nm (in-band of Yb3+), and at 406 nm (in-band of surface plasmon resonance given by the presence of SNP). The spectra as well as estimates for the basic parameters defining the lasing/amplifying potential of the glasses were studied as a function of SN concentration. The experimental results indicate that by increasing the SN content an enhancement of Er3+/Yb3+ fluorescence takes place.
ABSTRACT
The measurement of local temperature in nanoscale volumes is becoming a technological frontier. Photoluminescent nanoparticles and nanocolloids are the natural choice for nanoscale temperature probes. However, the influence of a surrounding liquid on the cryogenic behavior of oxidized Si-nanocrystals (Si-NCs) has never been investigated. In this work, the photoluminescence (PL) of oxidized Si-NCs/alcohol based nanocolloids is measured as a function of the temperature and the molecule length of monohydric alcohols above their melting-freezing point. The results unveil a progressive blue shift on the emission peak which is dependent on the temperature as well as the dielectric properties of the surrounding liquid. Such an effect is analyzed in terms of thermal changes of the Si-NCs bandgap, quantum confinement and the polarization effects of the embedding medium; revealing an important role of the dielectric constant of the surrounding liquid. These results are relevant because they offer a general insight to the fundamental behavior of photoluminescent nanocolloids under a cooling process and moreover, enabling PL tuning based on the dielectric properties of the surrounding liquid. Hence, the variables required to engineer PL of nanofluids are properly identified for use as temperature sensors at the nanoscale.
